Restaurants use food-holding cabinets to keep fried food (e.g., french fries, fried onions, and hash browns), rethermalized fried food (e.g., frozen pre-fried french fries that are baked in a convection oven shortly before serving), and non-fried food (e.g., bread) hot and crisp longer before serving the food to customers.
The typical frying process includes quickly heating food in a deep fryer at around and above 350 degrees F. This frying process quickly removes moisture from the surface of the fried food, giving it a hot, crisp appearance. The typical rethermalizing process includes baking frozen pre-cooked food in a baking oven, such as a convection oven, at around and above 350 degrees F.
Fried food quickly deteriorates once removed from its primary cooking source. The typical hold time for fried food is between 5 and 7 minutes. Rethermalized fried food typically has a hold time of only 3 to 5 minutes because its crisp surface (which acts as a barrier to loss of food heat and internal moisture) is thinner than that of recently fried food. Thereafter, the food becomes soft and develops a greasy appearance. Internal food moisture quickly creeps towards and softens the outer surface of the food, leading to many customer complaints about greasy and old food.
Patents such as U.S. Pat. Nos. 4,499,818; 6,114,659; and 6,261,621 describe the use of radiant heat and/or convection air to keep food hot and crisp. In 1985, U.S. Pat. No. 4,499,818 described the original idea of improving the holding time of fried food. U.S. Pat. No. 6,261,621 described a fried food-holding area having recirculating hot air forced on and about fried food items, a lower heater, and an upper heater made of overhead heating lamps. Many tests have shown that overhead heating lamps in any application cause fried food to quickly develop a moist outer surface. U.S. Pat. No. 6,114,659 described a food-holding bin having a base for holding food to be warmed. The base had first and second opposed edges, third and fourth opposed edges, and first and second end walls disposed at the first and second opposed edges of the base. Regions above the base and along the third and fourth opposed edges between the first and second end walls were substantially open to ambient atmosphere.